Example 1B - 3: Units and Carbon Dioxide Emissions

1B-3 :	Units and Carbon Dioxide Emissions	4 pts

A new, energy-efficient home refrigerator consumes about 350 kW-h of electricity per year. Assume the electricity is generated by burning fossil fuels. When fossil fuels like coal, oil, natural gas and gasoline are burned, most of

the carbon in the fuel burns completely to form carbon dioxide (CO₂). CO₂ is a greenhouse gas that contributes to global warming and that is undesirable. In a typical natural gas power plant, 0.5 kg of CO₂ is produced for each

kW-h of electricity generated. Consider a city with 500,000 homes with one refrigerator in each home. How much CO₂, in metric tons, is produced by the refrigerators in the city in one year?

Read:

This problem is all about unit conversions.
Keep careful track of units and it will not be difficult.
A kW-h is unit of energy. A Watt is energy per time and when you multiply by hours (time) you are left with units of energy. A kW-h is kW times hours. It is the amount of energy consumed in an hour by a device that uses 1 kW of power (1 kJ/s for 3600 sec).

Given:

m_CO2

0.5

kg CO₂ / kW-h

Power

350

kW-h/house/year

500000

houses

Find:

M_CO2

???

mton CO₂ / year

Assumptions:

None.

Equations / Data / Solve:

The total mass of CO₂ produced per year is the product of the rate of CO₂ production per kW-h, the rate at which power is used by each house and the number of houses.